1. Field of the Disclosure
The present invention relates generally to power converters, and more specifically, the invention relates to control circuits that regulate an output of a power converter.
2. Background
Many electrical devices such as cell phones, personal digital assistants (PDA's), laptops, etc. are powered by a source of relatively low-voltage DC power. Because power is generally delivered through a wall outlet as high-voltage AC power, a device, typically referred to as a power converter, is required to transform the high-voltage AC power to low-voltage DC power. The low-voltage DC power may be provided by the power converter directly to the device or it may be used to charge a rechargeable battery that, in turn, provides energy to the device, but which requires charging once stored energy is drained. Typically, the battery is charged with a battery charger that includes a power converter that meets constant current and constant voltage requirements required by the battery. In operation, a power converter may use a controller to regulate output power delivered to an electrical device, such as a battery, that may be generally referred to as a load. More specifically, the controller may be coupled to a sensor that provides feedback information of the output of the power converter in order to regulate power delivered to the load. The controller regulates power to the load by controlling a power switch to turn on and off in response to the feedback information from the sensor to transfer energy pulses to the output from a source of input power such as a power line.
Power converter control circuits may be used for a multitude of purposes and applications. There is a demand for control circuit functionality that can reduce the number of components outside the integrated control circuit. This reduction in external component count enables miniaturization of the power converter to improve portability, reduces the number of design cycles required to finalize a power converter design and also improves reliability of the end product. Furthermore, reduced component count can offer energy efficiency improvements in the operation of the power converter and can reduce the power converter cost. One aspect of the power converter offering the potential for component count reduction is in simplifying or removing the external circuitry previously required to detect fault conditions in the power converter.
In a power converter used for AC/DC power conversion, the output voltage is typically measured across the power supply output terminals to generate a feedback signal via a feedback circuit that is coupled to a control circuit on the input side of the power converter. Typically, the control circuit of the power converter regulates output power at the output terminals in response to the feedback signal. More specifically, the control circuit is responsive to the feedback signal to control switching of a power switch coupled to transfer energy from the input to the output of the power converter.
If the control circuit loses feedback information due to a fault, such as a short or open circuit in the feedback circuit, the power converter may deliver unregulated power which may cause damage to an electrical device coupled to the power converter or to the power converter itself.